Process for Producing Ethanol Using a Molar Excess of Hydrogen

ABSTRACT

The present invention relates to a process for the production of ethanol using a molar excess of hydrogen. A mixed feed of acetic acid and ethyl acetate is fed to a reactor to be converted to ethanol. Hydrogen flow is increased to avoid a negative conversion of ethyl acetate.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingethanol via the hydrogenation of acetic acid, ethyl acetate, andmixtures thereof. In particular, the present invention relates to theuse of a molar excess of hydrogen in the hydrogenation reaction.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosematerials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in organic feed stock prices contributes to fluctuations inthe cost of conventionally produced ethanol, making the need foralternative sources of ethanol production all the greater when feedstock prices rise. Starchy materials, as well as cellulose material, areconverted to ethanol by fermentation. However, fermentation is typicallyused for consumer production of ethanol, which is suitable for fuels orhuman consumption. In addition, fermentation of starchy or cellulosematerials competes with food sources and places restraints on the amountof ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. The hydrogenation of alkanoicacid, e.g., acetic acid, and optionally the respective esters, yields acrude ethanol product that comprises impurities, e.g., water, which areoften formed with ethanol or in side reactions. These impurities maylimit the production of ethanol and may require expensive and complexpurification trains to separate the impurities from the ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol product and a stream of acetic acidand ethyl acetate, which is recycled to the hydrogenation reactor.

Even in view of the conventional methods, the need remains for improvedprocesses for efficiently producing ethanol from acetic acid and/orethyl acetate.

SUMMARY OF THE INVENTION

The present invention relates to a process for the production ofethanol. The process comprises the step of reacting acetic acid, ethylacetate, and hydrogen and in the presence of a catalyst and underconditions effective to form a crude ethanol product. The crude ethanolproduct may comprise ethanol, acetic acid, ethyl acetate, and water.Preferably, the reaction is conducted in a reactor and a molar ratio ofhydrogen to acetic acid fed the reactor is greater than 12:1. In oneembodiment, the process may further comprise the step of maintaining thereactants in the reactor for a residence time less than 20 seconds. Theethyl acetate conversion may be greater than or equal to 0%, e.g., theconversion is not negative and there is not a net increase in ethylacetate under steady state conditions. The process further comprises thestep of recovering ethanol from the crude ethanol product.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of a hydrogenation/separation process inaccordance with an embodiment of the present invention.

FIG. 2 is a schematic diagram of a hydrogenation/separation process inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

Acetic acid and ethyl acetate may be reacted with hydrogen, e.g.,hydrogenated, to form a crude ethanol product. The crude ethanol productcomprises ethanol, unreacted acetic acid and ethyl acetate, as well asvarious impurities, e.g., water. These impurities 1) limit theproduction of ethanol and 2) require expensive and complex purificationtrains to separate the impurities from the ethanol. To increase reactionefficiencies and avoid the production of impurities, conversion of thereactants, e.g., acetic acid and ethyl acetate, into ethanol is desired.

In some cases, when the hydrogenation process is operating at steadystate, ethyl acetate is also fed to the reaction zone along with thefresh acetic acid. The ethyl acetate may be produced under hydrogenationconditions for reducing acetic acid to ethyl acetate and then recycledfrom the separation zone to the reaction zone as a vapor phase reactant.When the ethyl acetate in the vapor phase reactants is not consumed inthe reactor and ethyl acetate is continuously formed, the conversion ofethyl acetate would be negative, which is not desired. This may lead toa buildup of ethyl acetate that would reduce the efficiency of producingethanol.

Advantageously, the present invention may prevent negative conversion ofethyl acetate by increasing the hydrogen flow to the reactor relative tothe acetic acid flow and the ethyl acetate flow. The increased hydrogenflow reduces the residence time of the reactants in the reactor.Normally, a reduction in residence time may be expected to decrease theconversion of acetic acid and/or ethyl acetate. However, surprisinglyand unexpectedly, when hydrogen flow to the reactor is increased, amixed feed of acetic acid and ethyl acetate is able to maintain apositive (or a non-negative) conversion of ethyl acetate, e.g., at leastgreater than 0% or greater than or equal to 0%, thus avoiding negativeconversion of ethyl acetate. In addition, the conversion of acetic acidis not impacted by the increased flow of hydrogen and may be greaterthan 60%, e.g., greater than 70% or greater than 80%.

Accordingly, the present invention, in one embodiment, relates to aprocess for producing ethanol. The process comprises the step ofreacting acetic acid, ethyl acetate, and hydrogen to form a crudeethanol product. The crude ethanol product comprises ethanol, water,acetic acid and, ethyl acetate. The reaction may be conducted in areactor and in the presence of a catalyst. In preferred embodiments, dueto the increase flow of hydrogen, the gas hourly space velocity (GHSV)may be from 180 hr⁻¹ to 50,000, e.g., from 240 hr⁻¹ to 35,000 hr⁻¹, orfrom 240 hr⁻¹ to 3,000 hr⁻¹. For example, the residence time of thereactants in the reactor is less than 20 seconds, e.g., less than 17seconds or less than 15 seconds. The residence time may be from 0.1 to20 seconds, e.g., from 0.5 to 17 seconds or from 1 to 15 seconds. In oneembodiment, when four parallel reactors are employed, the residence timeindicates the total residence time for all four reactors, in total.

In addition, the increased hydrogen flow may also increase the molarratio of hydrogen to acetic acid in the reaction mixture that is fed tothe reactor. In one embodiment, the molar ratio of hydrogen to aceticacid may be greater than 12:1, e.g., greater than 15:1 or greater than20:1. Theoretically, the hydrogenation reaction consumes two moles ofhydrogen per mole of acetic acid and the feed to the reactor wouldcontain about 6.3 wt. % hydrogen. Due to the excess hydrogen with theincreased flow rates, the mole percentage of hydrogen is preferably atleast 20 wt. % hydrogen, e.g. at least 25 wt. % hydrogen or at least 30wt. % hydrogen.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. Preferably, the catalyst may be capableof converting acetic acid and ethyl acetate to ethanol underhydrogenation conditions. The materials, catalysts, reaction conditions,and separation processes that may be used in the hydrogenation of aceticacid and/or ethyl acetate are described further below.

The raw materials, acetic acid, ethyl acetate, and/or hydrogen, fed tothe reactor used in connection with the process of this invention may bederived from any suitable source including natural gas, petroleum, coal,biomass, and so forth. As examples, acetic acid may be produced viamethanol carbonylation, acetaldehyde oxidation, ethylene oxidation,oxidative fermentation, and anaerobic fermentation.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,132,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process and/or the methanolcarbonylation process may be derived partially or entirely from syngas.For example, the acetic acid may be formed from methanol and carbonmonoxide, both of which may be derived from syngas. The syngas may beformed by partial oxidation reforming or steam reforming, and the carbonmonoxide may be separated from syngas. Similarly, hydrogen that is usedin the step of hydrogenating the acetic acid to form the crude ethanolproduct may be separated from syngas. The syngas, in turn, may bederived from variety of carbon sources. The carbon source, for example,may be selected from the group consisting of natural gas, oil,petroleum, coal, biomass, and combinations thereof. Syngas or hydrogenmay also be obtained from bio-derived methane gas, such as bio-derivedmethane gas produced by landfills or agricultural waste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as aldehyde and/or ketones,such as acetaldehyde and acetone. Preferably, a suitable acetic acidfeed stream comprises one or more of the compounds selected from thegroup consisting of acetic acid, acetic anhydride, acetaldehyde, ethylacetate, and mixtures thereof. These other compounds may also behydrogenated in the processes of the present invention. In someembodiments, the presence of carboxylic acids, such as propanoic acid orits anhydride, may be beneficial in producing propanol. Water may alsobe present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the hydrogenation reactor without the need forcondensing the acetic acid and light ends or removing water, savingoverall processing costs.

FIG. 1 is a diagram of a process 100 in accordance with the presentinvention. Process 100 comprises reaction zone 102 and separation zone104. Reaction zone 102 comprises vaporizer 106 and reactor 108. Inreaction zone 102, hydrogen and acetic acid are fed to vaporizer 106 viahydrogen feed line 110 and acetic acid feed line 112, respectively. Insome embodiments, ethyl acetate may be fed to vaporizer 106 via ethylacetate feed line 114. Although FIG. 1 shows ethyl acetate being fed viaethyl acetate feed line 114, in one embodiment, ethyl acetate may be fedto reactor 108 from a recycle stream from separation zone 104. In oneembodiment, ethyl acetate may be present in the acetic acid feed. In oneembodiment, two or more of the reactant feed lines may be combined andfed to vaporizer 106 (not shown). In one embodiment, lines 112 and 114may be combined and fed to the vaporizer 106 (not shown). In oneembodiment, additional hydrogen may be fed to reactor 108 via a separatehydrogen feed line(s), e.g., hydrogen feed line(s) different fromhydrogen feed line 110 (not shown). In such cases, the additionalhydrogen feed line(s) may provide increased hydrogen flow to thereactor.

The acetic acid and ethyl acetate feeds in lines 112 and 114 may bepreheated to a temperature from 30° C. to 150° C., e.g., from 50° C. to125° C. or from 60° C. to 115° C. The hydrogen feed may be fed at apressure from 1200 kPa to 2100 kPa, e.g., from 1500 kPa to 2800 kPa, or1700 kPa to 2600 kPa.

In one embodiment, the flow of liquid acetic acid fed to the vaporizeris maintained at a relatively constant level as the process is operated.The molar ratio of hydrogen to acetic acid may be achieved by adjustingthe flow rate of hydrogen fed to vaporizer 106.

Vaporizer 106 may operate at a temperature of from 20° C. to 250° C. andat a pressure from 10 kPa to 2000 kPa. Vaporizer 106 produces vapor feedstream in line 116 by transferring the acetic acid, ethyl acetate, andwater from the liquid to gas phase below the boiling point of aceticacid in reactor 108 at the operating pressure of the reactor. In oneembodiment, the acetic acid in the liquid state is maintained at atemperature below 160° C., e.g., below 150° C. or below 130° C.Vaporizer 106 may be operated at a temperature of at least 118° C.Vaporizer 106 yields vapor feed stream 116 comprising hydrogen, aceticacid, and ethyl acetate, which is withdrawn from vaporizer 106 and fedto hydrogenation reactor 108.

The temperature of vapor feed stream 116 is preferably from 100° C. to350° C., e.g., from 120° C. to 210° C. or from 150° C. to 200° C. Insome embodiments, vapor feed stream 116 may comprise from 0.15 wt. % to25 wt. % water. In addition, although FIG. 1 shows line 116 beingdirected to the top of reactor 108, line 116 may be directed to theside, upper portion, or bottom of reactor 108.

The temperature of feed stream in line 116 is preferably from 100° C. to350° C., e.g., from 120° C. to 210° C. or from 150° C. to 200° C. Apreheater may be used to further heat feed stream 116 to the reactortemperature.

Any feed that is not vaporized is removed from vaporizer 106 in ablowdown stream and may be recycled or discarded thereto. The mass ratioof feed stream in line 116 to blowdown stream may be from 6:1 to 500:1,e.g., from 10:1 to 500:1, from 20:1 to 500:1 or from 50:1 to 500:1.

In reactor 108, acetic acid and/or ethyl acetate are hydrogenated toform a crude ethanol product comprising ethanol and other compounds suchas water, ethyl acetate, and acetic acid. The crude ethanol productexits reaction zone 102 via line 120. Separation zone 104 comprisesflasher 122 and one or more separation units, e.g. distillation columns,for recovering ethanol from the crude ethanol product. Exemplaryseparation zones are discussed below.

In one embodiment, one or more guard beds (not shown) may be usedupstream of the reactor, optionally upstream of the vaporizer 106, toprotect the catalyst from poisons or undesirable impurities contained inthe feed or return/recycle streams. Such guard beds may be employed inthe vapor or liquid streams. Suitable guard bed materials may include,for example, carbon, silica, alumina, ceramic, or resins. In one aspect,the guard bed media is functionalized, e.g., silver functionalized, totrap particular species such as sulfur or halogens.

The hydrogenation reactor, in some embodiments, may include a variety ofconfigurations using a fixed bed reactor or a fluidized bed reactor. Inmany embodiments of the present invention, an “adiabatic” reactor can beused; that is, there is little or no need for internal plumbing throughthe reaction zone to add or remove heat. In other embodiments, a radialflow reactor or reactors may be employed as the reactor, or a series ofreactors may be employed with or without heat exchange, quenching, orintroduction of additional feed material. Alternatively, a shell andtube reactor provided with a heat transfer medium may be used. In manycases, the reaction zone may be housed in a single vessel or in a seriesof vessels with heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation in the reactor may be carried out in either the liquidphase or vapor phase. Preferably, the reaction is carried out in thevapor phase under the following conditions. The reaction temperature mayrange from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225°C. to 200° C., or from 250° C. to 200° C. The pressure may range from 10kPa to 2000 kPa, e.g., from 50 kPa to 1200 kPa, or from 100 kPa to 1500kPa. The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Catalysts

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst in the reactor.

The catalysts of the invention preferably include at least one preciousmetal impregnated on the catalyst support. The precious metal may beselected, for example, from rhodium, rhenium, ruthenium, platinum,palladium, osmium, iridium and gold. Preferred precious metals for thecatalysts of the invention include palladium, platinum, and rhodium. Theprecious metal preferably is catalytically active in the hydrogenationof a carboxylic acid and/or its ester to the corresponding alcohol(s).The precious metal may be in elemental form or in molecular form, e.g.,an oxide of the precious metal. It is preferred that the catalystcomprises such precious metals in an amount less than 5 wt. %, e.g.,less than 3 wt. %, less than 1 wt. % or less than 0.5 wt. %. In terms ofranges, the catalyst may comprise the precious metal in an amount from0.05 to 10 wt. %, e.g. from 0.1 to 5 wt. %, or from 0.1 to 3 wt. %,based on the total weight of the catalyst.

In addition to the precious metal, the catalyst includes one or moreactive metals impregnated on the support. As used herein, the term“active metal” refers to a catalytically active metal, and may includeprecious or non-precious active metals. Thus, a catalyst comprising aprecious metal and an active metal may include: (i) one (or more)precious metals and one (or more) non-precious active metals, or (ii)may comprise two (or more) precious metals. Thus, precious metals areincluded herein as exemplary active metals. Further, it should beunderstood that use of the term “active metal” to refer to some metalsin the catalysts of the invention is not meant to suggest that theprecious metal that is also included in the inventive catalysts is notcatalytically active.

In one embodiment, the one or more active metals included in thecatalyst are selected from the group consisting of copper, iron, cobalt,vanadium, nickel, titanium, zinc, chromium, molybdenum, tungsten, tin,lanthanum, cerium, and manganese, or from any of the aforementionedprecious metals. Preferably, however, the one or more active metals donot include any precious metals. More preferably, the one or more activemetals are selected from the group consisting of copper, iron, cobalt,nickel, chromium, molybdenum, tungsten and tin, and more preferably theone or more active metals are selected from cobalt, tin and tungsten.The one or more active metals may be in elemental form or in molecularform, e.g., an oxide of the active metal, or a combination thereof. Thetotal weight of all the active metals, including the aforementionedprecious metal, present in the catalyst preferably is from 0.1 to 25 wt.%, e.g., from 0.5 to 15 wt. %, or from 1.0 to 10 wt. %. For purposes ofthe present specification, unless otherwise indicated, weight percent isbased on the total weight the catalyst including metal and support.

In some embodiments, the catalyst contains at least two active metals inaddition to the precious metal. The at least two active metals may beselected from any of the active metals identified above, so long as theyare not the same as the precious metal or each other. Additional activemetals may also be used in some embodiments. Thus, in some embodiments,there may be multiple active metals on the support in addition to theprecious metal.

Preferred bimetallic (precious metal+active metal) combinations for someexemplary catalyst compositions include platinum/tin,platinum/ruthenium, platinum/rhenium, platinum/cobalt, platinum/nickel,palladium/ruthenium, palladium/rhenium, palladium/cobalt,palladium/copper, palladium/nickel, ruthenium/cobalt, gold/palladium,ruthenium/rhenium, ruthenium/iron, rhodium/iron, rhodium/cobalt,rhodium/nickel and rhodium/tin. In some embodiments, the catalystcomprises three metals on a support, e.g., one precious metal and twoactive metals. Exemplary tertiary combinations may includepalladium/rhenium/tin, palladium/rhenium/cobalt,palladium/rhenium/nickel, palladium/cobalt/tin, platinum/tin/palladium,platinum/tin/rhodium, platinum/tin/gold, platinum/tin/iridium,platinum/cobalt/tin, platinum/tin/copper, platinum/tin/chromium,platinum/tin/zinc, platinum/tin/nickel, rhodium/nickel/tin,rhodium/cobalt/tin and rhodium/iron/tin. In one preferred embodiment,the tertiary combination comprises cobalt or tin or both cobalt and tin.In some embodiments, the catalyst may comprise more than three metals onthe support.

When the catalyst comprises a precious metal and one active metal on asupport, the active metal optionally is present in an amount from 0.1 to20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %. When thecatalyst comprises two or more active metals in addition to the preciousmetal, e.g., a first active metal and a second active metal, the firstactive metal may be present in the catalyst in an amount from 0.05 to 20wt. %, e.g. from 0.1 to 10 wt. %, or from 0.5 to 5 wt. %. The secondactive metal may be present in an amount from 0.05 to 20 wt. %, e.g.,from 0.1 to 10 wt. %, or from 0.5 to 5 wt. %. If the catalyst furthercomprises a third active metal, the third active metal may be present inan amount from 0.05 to 20 wt. %, e.g., from 0.05 to 10 wt. %, or from0.05 to 3 wt. %. The active metals may be alloyed with one another ormay comprise a non-alloyed metal solution, a metal mixture or be presentas one or more metal oxides.

The preferred metal ratios may vary somewhat depending on the activemetals used in the catalyst. In some embodiments, the mole ratio of theprecious metal to the one or more active metals is from 10:1 to 1:10,e.g., from 4:1 to 1:4, from 2:1 to 1:2 or from 1.5:1 to 1:1.5. Inanother embodiment, the precious metal may be present in an amount from0.1 to 5 wt. %, the first active metal in an amount from 0.5 to 20 wt. %and the second active metal in an amount from 0.5 to 20 wt. %, based onthe total weight of the catalyst. In another embodiment, the preciousmetal is present in an amount from 0.1 to 5 wt. %, the first activemetal in an amount from 0.5 to 1.5 wt. % and the second active metal inan amount from 0.5 to 1.5 wt. %, In one embodiment, the first and secondactive metals are present as cobalt and tin, and are present at a cobaltto tin molar ratio from 6:1 to 1:6 or from 3:1 to 1:3. In anotherembodiment, the cobalt and tin are present in substantially equimolaramounts.

The catalysts of the present invention comprise a suitable supportmaterial, preferably a modified support material. In one embodiment, thesupport material may be an inorganic oxide. In one embodiment, thesupport material may be selected from the group consisting of silica,alumina, titania, silica/alumina, pyrogenic silica, high purity silica,zirconia, carbon (e.g., carbon black or activated carbon) zeolites andmixtures thereof. Preferably, the support material comprises silica. Inpreferred embodiments, the support material is present in an amount from25 wt. % to 99 wt. %, e.g., from 30 wt. % to 98 wt. % or from 35 wt. %to 95 wt. %, based on the total weight of the catalyst.

In preferred embodiments, the support material comprises a silicaceoussupport material, e.g., silica, having a surface area of at least 50m²/g, e.g., at least 100 m²/g, at least 150 m²/g, at least 200 m²/g orat least 250 m²/g. In terms of ranges, the silicaceous support materialpreferably has a surface area from 50 to 600 m²/g, e.g., from 100 to 500m²/g or from 100 to 300 m²/g. High surface area silica, as usedthroughout the application, refers to silica having a surface area of atleast 250 m²/g. For purposes of the present specification, surface arearefers to BET nitrogen surface area, meaning the surface area asdetermined by ASTM D6556-04, the entirety of which is incorporatedherein by reference.

The preferred silicaceous support material also preferably has anaverage pore diameter from 5 to 100 nm, e.g., from 5 to 30 nm, from 5 to25 nm or from 5 to 10 nm, as determined by mercury intrusionporosimetry, and an average pore volume from 0.5 to 2.0 cm³/g, e.g.,from 0.7 to 1.5 cm³/g or from 0.8 to 1.3 cm³/g, as determined by mercuryintrusion porosimetry.

The morphology of the support material, and hence of the resultingcatalyst composition, may vary widely. In some exemplary embodiments,the morphology of the support material and/or of the catalystcomposition may be pellets, extrudates, spheres, spray driedmicrospheres, rings, pentarings, trilobes, quadrilobes, multi-lobalshapes, or flakes although cylindrical pellets are preferred.Preferably, the silicaceous support material has a morphology thatallows for a packing density from 0.1 to 1.0 g/cm³, e.g., from 0.2 to0.9 g/cm³ or from 0.3 to 0.8 g/cm³. In terms of size, the silica supportmaterial preferably has an average particle size, meaning the averagediameter for spherical particles or average longest dimension fornon-spherical particles, from 0.01 to 1.0 cm, e.g., from 0.1 to 0.7 cmor from 0.2 to 0.5 cm. Since the precious metal and the one or moreactive metals that are disposed on the support are generally in the formof very small metal (or metal oxide) particles or crystallites relativeto the size of the support, these metals should not substantially impactthe size of the overall catalyst particles. Thus, the above particlesizes generally apply to both the size of the support as well as to thefinal catalyst particles, although the catalyst particles are preferablyprocessed to form much larger catalyst particles, e.g., extruded to formcatalyst pellets.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint-Gobain N or Pro. The Saint-Gobain Nor Pro SS61138 silica contains approximately 95 wt. % high surface areasilica; a surface area of about 250 m²/g; a median pore diameter ofabout 12 nm; an average pore volume of about 1.0 cm³/g as measured bymercury intrusion porosimetry and a packing density of about 0.352g/cm³.

A preferred silica/alumina support material is KA-160 (Süd Chemie)silica spheres having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, in absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The support material preferably comprises a support modifier. A supportmodifier may adjust the acidity of the support material. In anotherembodiment, the support modifier may be a basic modifier that has a lowvolatility or no volatility. In one embodiment, the support modifiersare present in an amount from 0.1 wt. % to 50 wt. %, e.g., from 0.2 wt.% to 25 wt. %, from 0.5 wt. % to 15 wt. %, or from 1 wt. % to 12 wt. %,based on the total weight of the catalyst.

As indicated, the support modifiers may adjust the acidity of thesupport. For example, the acid sites, e.g., Brønsted acid sites or Lewisacid sites, on the support material may be adjusted by the supportmodifier to favor selectivity to ethanol during the hydrogenation ofacetic acid and/or esters thereof. The acidity of the support materialmay be adjusted by optimizing surface acidity of the support material.The support material may also be adjusted by having the support modifierchange the pKa of the support material. Unless the context indicatesotherwise, the acidity of a surface or the number of acid sitesthereupon may be determined by the technique described in F. Delannay,Ed., “Characterization of Heterogeneous Catalysts”; Chapter III:Measurement of Acidity of Surfaces, p. 370-404; Marcel Dekker, Inc.,N.Y. 1984, the entirety of which is incorporated herein by reference. Ingeneral, the surface acidity of the support may be adjusted based on thecomposition of the feed stream being sent to the hydrogenation processin order to maximize alcohol production, e.g., ethanol production.

In some embodiments, the support modifier may be an acidic modifier thatincreases the acidity of the catalyst. Suitable acidic support modifiersmay be selected from the group consisting of: oxides of Group IVBmetals, oxides of Group VB metals, oxides of Group VIB metals, oxides ofGroup VIIB metals, oxides of Group VIII metals, aluminum oxides, andmixtures thereof.

Acidic support modifiers include those selected from the groupconsisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃.Preferred acidic support modifiers include those selected from the groupconsisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, and Al₂O₃. The acidic modifiermay also include those selected from the group consisting of WO₃, MoO₃,V₂O₅, VO₂, V₂O₃, Nb₂O₅, Ta₂O₅, FeO, Fe₃O₄, Fe₂O₃, Cr₂O₃, MnO₂, CoO,Co₂O₃, and Bi₂O₃. Reduced tungsten oxides or molybdenum oxides may alsobe employed, such as, for example, one or more of W₂₀O₅₈, WO₂, W₄₉O₁₁₉,W₅₀O₁₄₈, W₁₈O₄₉, MO₉O₂₆, MO₈O₂₃, MO₅O₁₄, MO₁₇O₄₇, MO₄O₁₁, or MoO₂. Ithas now surprisingly and unexpectedly been discovered that the use ofsuch metal oxide support modifiers in combination with a precious metaland one or more active metals may result in catalysts havingmultifunctionality, and which may be suitable for converting acarboxylic acid, such as acetic acid, as well as corresponding estersthereof, e.g., ethyl acetate, to one or more hydrogenation products,such as ethanol, under hydrogenation conditions.

In some embodiments, the acidic support modifier comprises a mixed metaloxide comprising at least one of the active metals and an oxide anion ofa Group IVB, VB, VIB, VIII metal, such as tungsten, molybdenum,vanadium, niobium or tantalum. The oxide anion, for example, may be inthe form of a tungstate, molybdate, vanadate, or niobate. Exemplarymixed metal oxides include cobalt tungstate, copper tungstate, irontungstate, zirconium tungstate, manganese tungstate, cobalt molybdate,copper molybdate, iron molybdate, zirconium molybdate, manganesemolybdate, cobalt vanadate, copper vanadate, iron vanadate, zirconiumvanadate, manganese vanadate, cobalt niobate, copper niobate, ironniobate, zirconium niobate, manganese niobate, cobalt tantalate, coppertantalate, iron tantalate, zirconium tantalate, and manganese tantalate.It has now been discovered that catalysts containing such mixed metalsupport modifiers may provide the desired degree of multifunctionalityat increased conversion, e.g., increased ester conversion, and withreduced byproduct formation, e.g., reduced diethyl ether formation.

In one embodiment, the catalyst comprises from 0.25 to 1.25 wt. %platinum, from 1 to 10 wt. % cobalt, and from 1 to 10 wt. % tin on asilica or a silica-alumina support material. The support material maycomprise from 5 to 15 wt. % acidic support modifiers, such as WO₃, V₂O₅and/or MoO₃. In one embodiment, the acidic modifier may comprise cobalttungstate, e.g., in an amount from 5 to 15 wt. %.

In some embodiments, the modified support comprises one or more activemetals in addition to one or more acidic modifiers. The modified supportmay, for example, comprise one or more active metals selected fromcopper, iron, cobalt, vanadium, nickel, titanium, zinc, chromium,molybdenum, tungsten, tin, lanthanum, cerium, and manganese. Forexample, the support may comprise an active metal, preferably not aprecious metal, and an acidic or basic support modifier. Preferably, thesupport modifier comprises a support modifier metal selected from thegroup consisting of tungsten, molybdenum, vanadium, niobium, andtantalum. In this aspect, the final catalyst composition comprises aprecious metal, and one or more active metals disposed on the modifiedsupport. In a preferred embodiment, at least one of the active metals inthe modified support is the same as at least one of the active metalsdisposed on the support. For example, the catalyst may comprise asupport modified with cobalt, tin and tungsten (optionally as WO₃ and/oras cobalt tungstate). In this example, the catalyst further comprises aprecious metal, e.g., palladium, platinum or rhodium, and at least oneactive metal, e.g., cobalt and/or tin, disposed on the modified support.

Using an increase hydrogen flow and a mixed feed of acetic acid andethyl acetate, the hydrogenation in the first reactor may achievefavorable conversion of acetic acid and ethyl acetate. For purposes ofthe present invention, the term “conversion” refers to the amount ofacetic acid or ethyl acetate in the feed that is converted to a compoundother than acetic acid or ethyl acetate, respectively. Conversion isexpressed as a percentage based on acetic acid and/or ethyl acetate inthe feed. The conversion of acetic acid may be at least 10%, e.g., atleast 20%, at least 40%, at least 50%, at least 60%, at least 70% or atleast 80%. The conversion of ethyl acetate acid preferably is greaterthan 0%, meaning that more ethyl acetate is consumed than produced. Inother embodiments the ethyl acetate conversion is greater than or equalto 0%. During the hydrogenation of acetic acid, ethyl acetate may beproduced. Without consuming any ethyl acetate from the mixed vapor phasereactants, the conversion of ethyl acetate would be negative, meaningthat more ethyl acetate would be produced. However, for purposes of thepresent invention, enough of the ethyl acetate is consumed to at leastoffset the produced ethyl acetate. Thus, preferably conversion of ethylacetate may be greater than or equal to 0%, e.g., at least 5%, at least10%, at least 20%, or at least 35%. Although catalysts that have highconversions are desirable, especially acetic acid conversions that areat least 80% or at least 90%, in some embodiments a low acetic acidconversion may be acceptable at high selectivity for ethanol. It is, ofcourse, well understood that in many cases, it is possible to compensatefor low acetic acid conversion by appropriate recycle streams or use oflarger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted reactant,e.g., acetic acid or ethyl acetate. It should be understood that eachcompound converted from acetic acid or ethyl acetate has an independentselectivity and that selectivity is independent from conversion. Forexample, if 60 mole % of the converted acetic acid is converted toethanol, we refer to the ethanol selectivity as 60%. Total selectivityis based on the combined converted acetic acid and ethyl acetate.Preferably, the catalyst total selectivity to ethanol is at least 60%,e.g., at least 70%, or at least 80%. More preferably, in the reactor,the total selectivity to ethanol is at least 80%, e.g., at least 85% orat least 88%. Preferred embodiments of the hydrogenation process alsohave low selectivity to undesirable products, such as methane, ethane,and carbon dioxide. The selectivity to these undesirable productspreferably is less than 4%, e.g., less than 2% or less than 1%. Morepreferably, these undesirable products are present in undetectableamounts. Formation of alkanes may be low, and ideally less than 2%, lessthan 1%, or less than 0.5% of the acetic acid passed over the catalystis converted to alkanes, which have little value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the reactor, before any subsequent processing, suchas purification and separation, will typically comprise unreacted aceticacid, ethyl acetate, ethanol, and water. Exemplary compositional rangesfor the crude ethanol product are provided in Table 1. The “others”identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72 15 to70 25 to 65 Acetic Acid 0 to 90  0 to 50  0 to 35  0 to 15 Water 5 to 30 5 to 28 10 to 26 10 to 22 Ethyl Acetate 0 to 30  0 to 20  1 to 12  3 to10 Acetaldehyde 0 to 10 0 to 3 0.1 to 3   0.2 to 2   Others 0.1 to 10  0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product may comprise acetic acid inan amount less than 20 wt. %, e.g., of less than 15 wt. %, less than 10wt. % or less than 5 wt. %. In terms of ranges, the acetic acidconcentration of Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2wt. % to 15 wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt.%. In embodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is greater than 75%, e.g., greater than 85% orgreater than 90%.

Separation

Returning to FIG. 1, the hydrogenation reactor produces a crude ethanolproduct that is withdrawn, preferably continuously, from reactor 108 vialine 120 and directed to separation zone 104. Separation zone 104comprises flasher 122. The crude ethanol product may be condensed andfed to flasher 122, which, in turn, provides a vapor stream and a liquidstream. Flasher 122 may operate at a temperature of from 20° C. to 250°C., e.g., from 30° C. to 250° C. or from 60° C. to 200° C. The pressureof flasher 122 may be from 50 kPa to 2000 kPa, e.g., from 75 kPa to 1500kPa or from 100 kPa to 1000 kPa.

The vapor stream exiting flasher 122 may comprise hydrogen andhydrocarbons, at least a portion of which may be purged and/or returnedto reaction zone 102 via line 124. The returned portion of the vaporstream may pass through a compressor. The returned portion of the vaporstream and may be combined with the hydrogen feed line 110 and co-fed tovaporizer 106.

The liquid from flasher 122 is withdrawn and pumped as a feedcomposition via line 126 to the hydrogenation separation zone 104.Exemplary compositions of line 126 are provided in Table 2. It should beunderstood that liquid line 126 may contain other components, notlisted, such as additional components in the feed.

TABLE 2 FEED COMPOSITION Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Ethanol  5 to 72 10 to 70 15 to 65 Acetic Acid  <90  0 to 50  0 to 35Water  5 to 30  5 to 28 10 to 26 Ethyl Acetate  <30 0.001 to 25    1 to12 Acetaldehyde  <10 0.001 to 3    0.1 to 3   Acetal 0.01 to 10   0.001to 6    0.01 to 5   Acetone <5 0.0005 to 0.05  0.001 to 0.03  OtherAlcohols <5 <0.005 <0.001 Other Esters <5 <0.005 <0.001 Other Ethers <5<0.005 <0.001

The amounts indicated as less than (<) in the tables throughout thepresent application are preferably not present and if present may bepresent in trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 3 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol, 2-butanol or mixtures thereof. In one embodiment, the feedcomposition, e.g., line 126, may comprise propanol, e.g., isopropanoland/or n-propanol, in an amount from 0.001 to 0.1 wt. %, from 0.001 to0.05 wt. % or from 0.001 to 0.03 wt. %. It should be understood thatthese other components may be carried through in any of the distillateor residue streams described herein.

Optionally, the crude ethanol product may pass through one or moremembranes to separate hydrogen and/or other non-condensable gases. Inother optional embodiments, the crude ethanol product may be feddirectly to the acid separation column as a vapor feed and thenon-condensable gases may be recovered from the overhead of the column.

Ethanol produced by the reactor may be recovered using various differenttechniques. In FIG. 1, the separation of the crude ethanol product usestwo columns with an intervening water separation. In FIG. 2, theseparation of the crude ethanol product uses three columns. Otherseparation systems may also be used with embodiments of the presentinvention. In FIG. 2, the components of the reaction zone and theflasher are similar and perform similar functions to the correspondingcomponents in FIG. 1.

FIG. 1 illustrates an exemplary separation system. In FIG. 2, crudeethanol stream 126 is withdrawn from flasher 122 and pumped to the sideof first column 128. In one preferred embodiment, the hydrogenationreaction zone operates at above 80% acetic acid conversion, e.g., above90% conversion or above 99% conversion. Thus, the acetic acidconcentration in the liquid stream 126 may be low.

Liquid stream 126 is introduced in the middle or lower portion of firstcolumn 128, also referred to as an acid-water column. For purposes ofconvenience, the columns in each exemplary separation process, may bereferred as the first, second, third, etc., columns, but it isunderstood that first column 128 in FIG. 1 operates differently than thefirst column 228 of FIG. 2. In one embodiment, no entrainers are addedto first column 128. In FIG. 2, first column 128, water and unreactedacetic acid, along with any other heavy components, if present, areremoved from liquid stream 126 and are withdrawn, preferablycontinuously, as a first residue in line 130. Preferably, a substantialportion of the water in the crude ethanol product that is fed to firstcolumn 128 may be removed in the first residue, for example, up to about75% or to about 90% of the water from the crude ethanol product.Optionally, some of line 130, e.g., a small amount, may be also recycledto vaporizer the hydrogenation reaction zone. Optionally, at least aportion of residue in line 130 may be purged from the system. Reducingthe amount of heavies to be purged may improve efficiencies of theprocess while reducing byproducts. First column 128 also forms a firstdistillate, which is withdrawn in line 132.

When column 128 is operated under about 170 kPa, the temperature of theresidue exiting in line 130 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of thedistillate exiting in line 132 preferably is from 60° C. to 90° C.,e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 128 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 132 comprises water, in addition to ethanoland other organics. In terms of ranges, the concentration of water inthe first distillate in line 132 preferably is from 4 wt. % to 38 wt. %,e.g., from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. A portion offirst distillate in line 132 may be condensed and refluxed, for example,at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to2:1. It is understood that reflux ratios may vary with the number ofstages, feed locations, column efficiency and/or feed composition.Operating with a reflux ratio of greater than 3:1 may be less preferredbecause more energy may be required to operate the first column 128. Thecondensed portion of the first distillate in line 134 may optionallyalso be combined with line 136, discussed below, and fed to secondcolumn 138.

The remaining portion of the first distillate in line 132 is fed towater separation unit 140. Water separation unit 140 may be anadsorption unit, membrane, molecular sieves, extractive columndistillation, or a combination thereof. A membrane or an array ofmembranes may also be employed to separate water from the distillate.The membrane or array of membranes may be selected from any suitablemembrane that is capable of removing a permeate water stream from astream that also comprises ethanol and ethyl acetate.

In a preferred embodiment, water separator 140 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure of from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. ThePSA unit may comprise two to five beds. Water separator 140 may removeat least 95% of the water from the portion of first distillate in line132, and more preferably from 99% to 99.99% of the water from the firstdistillate, in a water stream 142. All or a portion of water stream 142may be returned to column 128 in line 144, where the water preferably isultimately recovered from column 128 in the first residue in line 130.Additionally or alternatively, all or a portion of water stream 142 maybe purged. The remaining portion of first distillate 132 exits the waterseparator 140 as ethanol mixture stream 146. Ethanol mixture stream 146may have a low concentration of water of less than 10 wt. %, e.g., lessthan 6 wt. % or less than 2 wt. %. Exemplary components of ethanolmixture stream 146 and first residue in line 130 are provided in Table 2below. It should also be understood that these streams may also containother components, not listed, such as components derived from the feed.

TABLE 2 FIRST COLUMN 128 WITH PSA (FIG. 1) Conc. (wt. %) Conc. (wt. %)Conc. (wt. %) Ethanol Mixture Stream Ethanol 20 to 95 30 to 95 40 to 95Water <10 0.01 to 6   0.1 to 2   Acetic Acid <2  0.001 to 0.5  0.01 to0.2  Ethyl Acetate <60  1 to 55  5 to 55 Acetaldehyde <10 0.001 to 5   0.01 to 4   Acetal  <0.1 <0.1 <0.05 Acetone   <0.05 0.001 to 0.03   0.01to 0.025 Residue Acetic Acid <90  1 to 50  2 to 35 Water 30 to 99 45 to95 60 to 90 Ethanol <1  <0.9 <0.3 

Preferably, ethanol mixture stream 136 is not returned or refluxed tofirst column 128. The condensed portion of the first distillate in line134 may be combined with ethanol mixture stream 136 to control the waterconcentration fed to the second column 138. For example, in someembodiments the first distillate may be split into equal portions, whilein other embodiments, all of the first distillate may be condensed orall of the first distillate may be processed in the water separationunit. In FIG. 1, the condensed portion in line 134 and ethanol mixturestream 136 are co-fed to second column 138. In other embodiments, thecondensed portion in line 134 and ethanol mixture stream 136 may beseparately fed to second column 138. The combined distillate and ethanolmixture has a total water concentration of greater than 0.5 wt. %, e.g.,greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, thetotal water concentration of the combined distillate and ethanol mixturemay be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10wt. %.

The second column 138 in FIG. 1, also referred to as the “light endscolumn,” removes ethyl acetate and acetaldehyde from the firstdistillate in line 132 and/or ethanol mixture stream 136. Ethyl acetateand acetaldehyde are removed as a second distillate in line 146 andethanol is removed as the second residue in line 148. Optionally, thesecond distillate in line 146 may be recycled to reaction zone 102 andfed to reactor 208 (not shown). Second column 138 may be a tray columnor packed column. In one embodiment, second column 138 is a tray columnhaving from 5 to 70 trays, e.g., from 15 to 50 trays or from 20 to 45trays.

Second column 138 operates at a pressure ranging from 0.1 kPa to 510kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa. Althoughthe temperature of second column 138 may vary, when at about 20 kPa to70 kPa, the temperature of the second residue exiting in line 148preferably is from 30° C. to 75° C., e.g., from 35° C. to 70° C. or from40° C. to 65° C. The temperature of the second distillate exiting inline 146 preferably is from 20° C. to 55° C., e.g., from 25° C. to 50°C. or from 30° C. to 45° C.

The total concentration of water fed to second column 138 preferably isless than 10 wt. %, as discussed above. When first distillate in line132 and/or ethanol mixture stream comprises minor amounts of water,e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may befed to the second column 138 as an extractive agent in the upper portionof the column, e.g., via extractive agent feed 150. A sufficient amountof water is preferably added via the extractive agent such that thetotal concentration of water fed to second column 138 is from 1 to 10wt. % water, e.g., from 2 to 6 wt. %, based on the total weight of allcomponents fed to second column 138. If the extractive agent compriseswater, the water may be obtained from an external source or from aninternal return/recycle line from one or more of the other columns orwater separators.

Suitable extractive agents may also include, for example,dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane, chlorinatedparaffins, or a combination thereof. When extractive agents are used, asuitable recovery system, such as a further distillation column, may beused to recycle the extractive agent.

Exemplary components for the second distillate and second residuecompositions for the second column 138 are provided in Table 3, below.It should be understood that the distillate and residue may also containother components, not listed in Table 3.

TABLE 3 SECOND COLUMN 138 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethyl Acetate  5 to 90 10 to 80 15 to 75Acetaldehyde <60  1 to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to35   Water <20 0.01 to 10   0.1 to 5   Second Residue Ethanol   80 to99.5 85 to 97 60 to 95 Water <20 0.001 to 15   0.01 to 10   EthylAcetate <1  0.001 to 2    0.001 to 0.5  Acetic Acid  <0.5 <0.01 0.001 to0.01 

The second residue in FIG. 1 comprises one or more impurities selectedfrom the group consisting of ethyl acetate, acetic acid, acetaldehyde,and diethyl acetal. The second residue may comprise at least 100 wppm ofthese impurities, e.g., at least 250 wppm or at least 500 wppm. In someembodiments, the second residue may contain substantially no ethylacetate or acetaldehyde.

The second distillate in line 146, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 1, for example, ata reflux ratio of from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3to 3:1. In one aspect, not shown, the second distillate 146 or a portionthereof may be returned to the hydrogenation reactor. The ethyl acetateand/or acetaldehyde in the second distillate may be further reacted inthe hydrogenation reactor.

In one embodiment, the second distillate in line 146 and/or a refinedsecond distillate, or a portion of either or both streams, may befurther separated to produce an acetaldehyde-containing stream and anethyl acetate-containing stream. This may allow a portion of either theresulting acetaldehyde-containing stream or ethyl acetate-containingstream to be recycled to the hydrogenation reactor while purging theother stream. The purge stream may be valuable as a source of eitherethyl acetate and/or acetaldehyde.

FIG. 2 illustrates another exemplary separation system. In FIG. 2, crudeethanol stream 226 is withdrawn from a flasher 222 and pumped to theside of first column 228. In one preferred embodiment, the hydrogenationreaction zone operates at above 80% acetic acid conversion, e.g., above90% conversion or above 99% conversion. Thus, the acetic acidconcentration in the liquid stream 226 may be low.

In the exemplary embodiment shown in FIG. 2, liquid stream 226 isintroduced in the lower part of first column 228, e.g., lower half ormiddle third. In one embodiment, no entrainers are added to first column228. In first column 228, a weight majority of the ethanol, water,acetic acid, and other heavy components, if present, are removed fromliquid stream 226 and are withdrawn, preferably continuously, as residuein line 230.

First column 228 also forms an overhead distillate, which is withdrawnin line 232, and which may be condensed and refluxed, for example, at aratio of from 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 1:5 to 5:1.The overhead distillate in stream 232 preferably comprises a weightmajority of the ethyl acetate from liquid stream 226. Overheaddistillate in stream 232 may be combined with a recycle line from column234 as discussed below, and returned to the reaction zone.

When column 228 is operated under about 170 kPa, the temperature of theresidue exiting in line 230 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The base of column 228may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, water, and acetic acid, therebyproviding an energy efficiency advantage. The temperature of thedistillate exiting in line 232 from column 228 preferably at 170 kPa isfrom 75° C. to 100° C., e.g., from 75° C. to 83° C. or from 81° C. to84° C. In some embodiments, the pressure of first column 228 may rangefrom 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to375 kPa. Exemplary components of the distillate and residue compositionsfor first column 228 are provided in Table 4 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 4.

TABLE 4 FIRST COLUMN 228 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethyl Acetate 10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1to 70  0.2 to 65  0.5 to 65  Acetal <0.1  <0.1 <0.05 Acetone <0.05 0.001to 0.03   0.01 to 0.025 Ethanol  3 to 55  4 to 50  5 to 45 Water 0.1 to20   1 to 15  2 to 10 Acetic Acid <2   <0.1 <0.05 Residue Acetic Acid0.01 to 35   0.1 to 30  0.2 to 25  Water  5 to 40 10 to 35 15 to 30Ethanol 10 to 75 15 to 70 20 o 65

In an embodiment of the present invention, column 228 may be operated ata temperature where most of the water, ethanol, and acetic acid areremoved from the residue stream and only a small amount of ethanol andwater is collected in the distillate stream due to the formation ofbinary and tertiary azeotropes. The weight ratio of water in the residuein line 230 to water in the distillate in line 232 may be greater than1:1, e.g., greater than 2:1. The weight ratio of ethanol in the residueto ethanol in the distillate may be greater than 1:1, e.g., greater than2:1

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in the hydrogenation reactor. In oneembodiment, when the conversion is high, e.g., greater than 90%, theamount of acetic acid in the first residue may be less than 10 wt. %,e.g., less than 5 wt. % or less than 2 wt. %. In other embodiments, whenthe conversion is lower, e.g., less than 90%, the amount of acetic acidin the first residue may be greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g.,comprising less than 1000 wppm, less than 500 wppm or less than 100 wppmacetic acid. The distillate may be purged from the system or recycled inwhole or part to the hydrogenation reactor. In some embodiments, thedistillate may be further separated, e.g., in a distillation column (notshown), into an acetaldehyde stream and an ethyl acetate stream. Eitherof these streams may be returned to the hydrogenation reactor orseparated as a separate product.

Some species, such as acetals, may decompose in first column 228 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue.

To recover ethanol, the residue in line 230 may be further separated insecond column 234, also referred to as an “acid separation column.” Anacid separation column may be used when the acetic acid concentration inthe first residue is greater than 1 wt. %, e.g., greater than 5 wt. %.The first residue in line 230 is introduced to second column 234preferably in the top part of column 234, e.g., top half or top third.Second column 234 yields a second residue in line 236 comprising aceticacid and water, and a second distillate in line 238 comprising ethanol.

Second column 234 may be a tray column or packed column. In oneembodiment, second column 234 is a tray column having from 5 to 150trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although thetemperature and pressure of second column 234 may vary, when atatmospheric pressure the temperature of the second residue exiting inline 236 preferably is from 95° C. to 130° C., e.g., from 100° C. to125° C. or from 110° C. to 120° C. The temperature of the seconddistillate exiting in line 238 preferably is from 60° C. to 105° C.,e.g., from 75° C. to 100° C. or from 80° C. to 100° C. The pressure ofsecond column 234 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to475 kPa or from 1 kPa to 375 kPa. Exemplary components for thedistillate and residue compositions for second column 234 are providedin Table 5 below. It should be understood that the distillate andresidue may also contain other components, not listed in Table 5.

TABLE 5 SECOND COLUMN 234 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethanol   70 to 99.9 75 to 98 80 to 95 EthylAcetate  <10 0.001 to 5    0.01 to 3   Acetaldehyde <5 0.001 to 1   0.005 to 0.5  Water 0.1 to 30   1 to 25  5 to 20 Second Residue AceticAcid 0.1 to 45  0.2 to 40  0.5 to 35  Water   45 to 99.9   55 to 99.8  65 to 99.5 Ethyl Acetate <2 <1 <0.5 Ethanol <5 0.001 to 5    <2  

The weight ratio of ethanol in the second distillate in line 238 toethanol in the second residue in line 236 preferably is at least 35:1.In one embodiment, the weight ratio of water in the second residue 236to water in the second distillate 238 is greater than 2:1, e.g., greaterthan 4:1 or greater than 6:1. In addition, the weight ratio of aceticacid in the second residue 236 to acetic acid in the second distillate238 preferably is greater than 10:1, e.g., greater than 15:1 or greaterthan 20:1. Preferably, the second distillate in line 238 issubstantially free of acetic acid and may only contain, if any, traceamounts of acetic acid.

As shown, the second distillate in line 238 is fed to optional thirdcolumn 240, e.g., ethanol product column, for separating the seconddistillate into a third distillate (ethyl acetate distillate) in line242 and a third residue (ethanol residue) in line 344. Although FIG. 2shows 240, column 240 is not required to implement the presentinvention. In one embodiment (not shown) the separation zone comprises afirst column, e.g., column 228, and second column, e.g., column 234, anddoes not include a third column. Second distillate in line 238 may beintroduced into the lower part of column 240, e.g., lower half or lowerthird. Third distillate 242 is preferably refluxed, for example, at areflux ratio greater than 2:1, e.g., greater than 5:1 or greater than10:1. Additionally, at least a portion of third distillate 242 may bepurged. Third column 240 is preferably a tray column as described hereinand preferably operates at atmospheric pressure. The temperature of thethird residue exiting from third column 240 preferably is from 60° C. to110° C., e.g., from 70° C. to 100° C. or from 75° C. to 95° C. Thetemperature of the third distillate exiting from third column 240preferably is from 70° C. to 115° C., e.g., from 80° C. to 110° C. orfrom 85° C. to 105° C., when the column is operated at atmosphericpressure.

The remaining water from the second distillate in line 238 may beremoved in further embodiments of the present invention. Depending onthe water concentration, the ethanol product may be derived from thesecond distillate in line 238. Some applications, such as industrialethanol applications, may tolerate water in the ethanol product, whileother applications, such as fuel applications, may require an anhydrousethanol. The amount of water in the distillate of line 238 may be closerto the azeotropic amount of water, e.g., at least 4 wt. %, preferablyless than 20 wt. %, e.g., less than 12 wt. % or less than 7.5 wt. %.Water may be removed from the second distillate in line 238 usingseveral different separation techniques as described herein.Particularly preferred techniques include the use of distillationcolumn, membranes, adsorption units, and combinations thereof.

The columns shown in FIGS. 1 and 2 may comprise any distillation columncapable of performing the desired separation and/or purification. Eachcolumn preferably comprises a tray column having from 1 to 150 trays,e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays.The trays may be sieve trays, fixed valve trays, movable valve trays, orany other suitable design known in the art. In other embodiments, apacked column may be used. For packed columns, structured packing orrandom packing may be employed. The trays or packing may be arranged inone continuous column or they may be arranged in two or more columnssuch that the vapor from the first section enters the second sectionwhile the liquid from the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 2000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the ethanol product. Exemplary finished ethanolcompositional ranges are provided below in Table 6.

TABLE 6 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12   1 to 9 3to 8 Acetic Acid <1   <0.1 <0.01 Ethyl Acetate <2   <0.5 <0.05 Acetal<0.05  <0.01  <0.005 Acetone <0.05  <0.01  <0.005 Isopropanol <0.5  <0.1<0.05 n-propanol <0.5  <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be higher than indicated in Table 11, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0020002 and 2010/0020001, the entireties of which is incorporatedherein by reference. A zeolite catalyst, for example, may be employed asthe dehydration catalyst. Preferably, the zeolite has a pore diameter ofat least about 0.6 nm, and preferred zeolites include dehydrationcatalysts selected from the group consisting of mordenites, ZSM-5, azeolite X and a zeolite Y. Zeolite X is described, for example, in U.S.Pat. No. 2,882,144 and zeolite Yin U.S. Pat. No. 3,130,007, theentireties of which are hereby incorporated herein by reference.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited herein and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising: (a) reactingacetic acid, ethyl acetate, and hydrogen in a reactor and in thepresence of a catalyst under conditions effective to form a crudeethanol product comprising ethanol, acetic acid, ethyl acetate, andwater; and (b) recovering ethanol from the crude ethanol product;wherein the molar ratio of hydrogen to acetic acid fed the reactor isgreater than 12:1; and wherein ethyl acetate conversion is greater thanor equal to 0%.
 2. The process of claim 1, further comprising the stepof: maintaining the reactants in the reactor for a residence time lessthan 20 seconds.
 3. The process of claim 2, wherein the residence timeis less than 17 seconds.
 4. The process of claim 1, wherein acetic acidconversion is greater than 60%.
 5. The process of claim 1, whereinacetic acid conversion is greater than 70%.
 6. The process of claim 1,wherein the acetic acid, the ethyl acetate, and the hydrogen comprise areaction mixture and wherein the reaction mixture comprises greater than20 wt. % hydrogen.
 7. The process of claim 1, wherein the acetic acid isformed from methanol and carbon monoxide, wherein each of the methanol,the carbon monoxide, and hydrogen for the hydrogenating step is derivedfrom syngas, and wherein the syngas is derived from a carbon sourceselected from the group consisting of natural gas, oil, petroleum, coal,biomass, and combinations thereof.
 8. The process of claim 1, whereinthe catalyst comprises one or more precious metals on a support.
 9. Theprocess of claim 8, wherein the one or more precious metals is selectedfrom the group consisting of rhodium, platinum, palladium, osmium,iridium, gold, rhenium, and ruthenium.
 10. The process of claim 8,wherein the catalyst further comprises one or more active metalsdifferent from the one or more precious metals.
 11. The process of claim10, wherein the one or more active metals is selected from the groupconsisting of copper, iron, cobalt, vanadium, nickel, titanium, zinc,chromium, molybdenum, tungsten, tin, lanthanum, cerium, manganese,rhodium, platinum, palladium, osmium, iridium, gold, rhenium, andruthenium.
 12. The process of claim 10, wherein the preciousmetal/active metal combination is selected from the group consisting ofplatinum/tin, platinum/ruthenium, platinum/rhenium, platinum/cobalt,platinum/nickel, palladium/ruthenium, palladium/rhenium,palladium/cobalt, palladium/copper, palladium/nickel, ruthenium/cobalt,gold/palladium, ruthenium/rhenium, ruthenium/iron,palladium/rhenium/tin, palladium/rhenium/cobalt,palladium/rhenium/nickel, palladium/cobalt/tin, platinum/tin/palladium,platinum/tin/rhodium, platinum/tin/gold, platinum/tin/iridium,platinum/cobalt/tin, platinum/tin/copper, platinum/tin/chromium,platinum/tin/zinc, and platinum/tin/nickel.
 13. The process of claim 8,wherein the support is selected from the group consisting of silica,alumina, titania, silica/alumina, calcium metasilicate, pyrogenicsilica, high purity silica, zirconia, carbon, zeolites and mixturesthereof.
 14. The process of claim 8, wherein the catalyst furthercomprises a support modifier
 15. The catalyst of claim 14, wherein thesupport modifier is selected from the group consisting of oxides ofGroup IVB metals, oxides of Group VB metals, oxides of Group VIB metals,oxides of Group VIIB metals, oxides of Group VIII metals, aluminumoxides, and mixtures thereof.
 16. The catalyst of claim 14, wherein thesupport modifier is selected from the group consisting of TiO₂, ZrO₂,Nb₂O₅, Ta₂O₅, Al₂O₃, B₂O₃, P₂O₅, Sb₂O₃, WO₃, MoO₃, V₂O₅, Nb₂O₅, Ta₂O₅,Fe₂O₃, Cr₂O₃, MnO₂, CuO, Co₂O₃, and Bi₂O₃.
 17. The catalyst of claim 14,wherein the support modifier is selected from the group consisting of(i) alkaline earth metal oxides, (ii) alkali metal oxides, (iii)alkaline earth metal metasilicates, (iv) alkali metal metasilicates, (v)Group IIB metal oxides, (vi) Group IIB metal metasilicates, (vii) GroupIIIB metal oxides, (viii) Group IIIB metal metasilicates, and mixturesthereof.
 18. The process of claim 1, wherein the reactants are fed tothe reactor at a gas hourly space velocity (GHSV) from 180 hr⁻¹ to50,000 hr⁻¹.
 19. A process for producing ethanol, comprising: (a)reacting acetic acid, ethyl acetate, and hydrogen in a reactor and inthe presence of a catalyst under conditions effective to form a crudeethanol product comprising ethanol, acetic acid, ethyl acetate, andwater, wherein the molar ratio of hydrogen to acetic acid fed thereactor is greater than 12:1, and wherein ethyl acetate conversion isgreater than or equal to 0%; (b) separating at least a portion of thecrude ethanol product in a first distillation column to yield a firstresidue comprising acetic acid and a first distillate comprisingethanol, ethyl acetate, and water; (c) removing water from at least aportion of the first distillate to yield an ethanol mixture streamcomprising less than 10 wt. % water; and (d) separating a portion of theethanol mixture stream in a second distillation column to yield a secondresidue comprising ethanol and a second distillate comprising ethylacetate.
 20. The process of claim 19, wherein a portion of the seconddistillate is returned to the reactor.
 21. A process for producingethanol, comprising: (a) reacting acetic acid, ethyl acetate, andhydrogen in a reactor and in the presence of a catalyst under conditionseffective to form a crude ethanol product comprising ethanol, aceticacid, ethyl acetate, and water, wherein the molar ratio of hydrogen toacetic acid fed the reactor is greater than 12:1, and wherein ethylacetate conversion is greater than or equal to 0%; (b) separating aportion of the crude ethanol product in a first distillation column toyield a first distillate comprising ethyl acetate and acetaldehyde, anda first residue comprising ethanol, ethyl acetate, acetic acid andwater; (c) separating a portion of the first residue in a seconddistillation column to yield a second residue comprising acetic acid andwater and a second distillate comprising ethanol and ethyl acetate; and(d) separating a portion of the second distillate in a thirddistillation column to yield a third residue comprising ethanol and athird distillate comprising ethyl acetate.
 22. The process of claim 21,wherein a portion of the first distillate is returned to the reactor.23. The process of claim 21, wherein a portion of the third distillateis returned to the reactor.